ADR512 Data Sheet
Rev. A | Page 8 of 12
APPLICATIONS SECTION
The ADR512 is a 1.2 V precision shunt voltage reference. It is
designed to operate without an external output capacitor
between the positive and negative terminals for stability. An
external capacitor can be used for additional filtering of the
supply.
As with all shunt voltage references, an external bias resistor
(R
BIAS
) is required between the supply voltage and the ADR512
(see Figure 2). R
BIAS
sets the current that is required to pass
through the load (I
L
) and the ADR512 (I
Q
). The load and the
supply voltage can vary, thus R
BIAS
is chosen based on
• R
BIAS
must be small enough to supply the minimum I
Q
current to the ADR512 even when the supply voltage is at
its minimum and the load current is at its maximum value.
• R
BIAS
also needs to be large enough so that I
Q
does not
exceed 10 mA when the supply voltage is at its maximum
and the load current is at its minimum.
Given these conditions, R
BIAS
is determined by the supply
voltage (V
S
), the load and operating current (I
L
and I
Q
) of the
ADR512, and the ADR512’s output voltage.
R
BIAS
= (V
S
− V
OUT
)/(I
L
+ I
Q
) (3)
ADJUSTABLE PRECISION VOLTAGE SOURCE
The ADR512, combined with a precision low input bias op amp
such as the AD8610, can be used to output a precise adjustable
voltage. Figure 11 illustrates the implementation of this application
using the ADR512.
The output of the op amp, V
OUT
, is determined by the gain of the
circuit, which is completely dependent on resistors R2 and R1.
(4)
An additional capacitor in parallel with R2 can be added to
filter out high frequency noise. The value of C2 is dependent on
the value of R2.
ADR512
AD8610
R1
R2
C2 (OPTIONAL)
V
CC
R
BIAS
1.2V
V
OUT
= 1.2V
(1 + R2/R1)
03700-0
11
Figure 11. Adjustable Precision Voltage Source
OUTPUT VOLTAGE TRIM
Using a mechanical or digital potentiometer, the output voltage
of the ADR512 can be trimmed ±0.5%. The circuit in Figure 12
illustrates how the output voltage can be trimmed, using a 10 kΩ
potentiometer.
ADR512
R1
100kΩ
V
CC
R
BIAS
V
OUT
POT
50kΩ
03700-012
Figure 12. Output Voltage Trim
USING THE ADR512 WITH PRECISION DATA
CONVERTERS
The compact ADR512 package and the device’s low minimum
operating current requirement make it ideal for use in battery
powered portable instruments, such as the AD7533 CMOS
multiplying DAC, that use precision data converters.
Figure 13 shows the ADR512 serving as an external reference to
the AD7533, a CMOS multiplying DAC. Such a DAC requires a
negative voltage input in order to provide a positive output
range. In this application, the ADR512 is supplying a −1.2 V
reference to the REF input of the AD7533.
ADR512
AD7533
V
OUT
= 0V TO 1.2V
V
DD
–V
DD
R2
G
N
9
LSB
0
MSB
+
–
+
–
1
1
3
2 1 15
03700-013
Figure 13. ADR512 as a Reference for a 10-Bit CMOS DAC (AD7533)
